Photopolymerizable inkjet ink

ABSTRACT

To provide a photopolymerizable inkjet ink, which contains photopolymerizable monomers containing at least one selected from the following compound group (A) compounds of which are negative for skin sensitization, and at least one selected from the following compound group (B) compounds of which are negative for skin sensitization, wherein the compound group (A) is a compound group consisting of caprolactone-modified dipentaerythritol hexaacrylate, polyethoxylated tetramethylol methane tetraacrylate, ethylene oxide-modified bisphenol A diacrylate, caprolactone-modified hydroxy pivalic acid neopentyl glycol diacrylate, polypropylene glycol diacrylate [CH 2 ═CH—CO—(OC 3 H 6 )n-OCOCH═CH 2  (n≈12)], hydroxyethyl acryl amide, trimethylol propane trimethacrylate, and tricyclodecane dimethanol dimethacrylate, and the compound group (B) is a compound group consisting of ethylene oxide-modified phenolacrylate, isostearyl acrylate, ethylene oxide-modified trimethylol propane trimethacrylate, stearyl methacrylate, and glycerin dimethacrylate.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a 35 U.S.C. §371 national stage patentapplication of International patent application PCT/JP2012/078555, filedon Oct. 30, 2012, published as WO/2013/069580 on May 16, 2013, the textof which is incorporated by reference, and claims the benefit of thefiling date of Japanese application No. 2011-243072, filed on Nov. 7,2011, the text of which is also incorporated by reference.

TECHNICAL FIELD

The present invention relates to a photopolymerizable inkjet ink.

BACKGROUND ART

Photopolymerizable inkjet inks using (meth)acrylic acid esters andphotopolymerizable inkjet inks using a combination of (meth)acrylic acidesters and vinyl ethers have been widely known (see PTL 1 etc.).

However, many of monomers used in conventional photopolymerizable inkjetinks are toxic. Especially, most of (meth)acrylic acid esters, which arereadily available with low cost, have high toxicity in terms of skinsensitivity, which causes allergy reactions with skin upon contact withthem. Conventional art has not provided any solution to this problem.

CITATION LIST Patent Literature

PTL 1: Japanese Patent Application Laid-Open (JP-A) No. 2004-526820

SUMMARY OF INVENTION Technical Problem

The present invention aims to solve the aforementioned problems in theart, and to achieve the following object. An object of the presentinvention is to provide a photopolymerizable inkjet ink, which has noproblem of skin sensitization, and achieve both low viscosity andimproved curing property.

Solution to Problem

As a result of the studies conducted by the present inventors, they havefound several (meth)acrylic acids and (meth)acryl amides, which do nothave a problem of skin sensitization. When an ink is produced by usingthese monomers and imparting curing property to a level of practicaluse, however, it has been found that a resulting ink has high viscositycompared to commonly used inkjet inks. Therefore, such ink cannot beejected as inkjets without use of an ejection heat capable of heating tothe temperature high enough to make the ink low viscous. Moreover, it isnecessary to set the internal pressure of the head considerably high toeject the ink. Accordingly, there are problem with the aforementionedink that stable ejection performances cannot be obtained easily.

The present inventors have conducted diligent studies to solve theaforementioned various problems and to achieve the aforementionedobject, and the studies have lead to the following insights. Based onsuch insights, the present invention has been accomplished. Namely, theinsights of the present inventors are that a photopolymerizable inkjetink containing at least one selected from the following compound group(A), compounds of which are negative for skin sensitization, and atleast one selected from the following compound group (B), compounds ofwhich are negative for skin sensitization, has not a problem of skinsensitization, and can achieve both low viscosity and improved curingproperty.

The present invention is based upon the insights of the presentinventors, and means for solving the aforementioned problems are asfollows:

A photopolymerizable inkjet ink, which contains:

photopolymerizable monomers containing at least one selected from thefollowing compound group (A) compounds of which are negative for skinsensitization, and at least one selected from the following compoundgroup (B) compounds of which are negative for skin sensitization,

wherein the compound group (A) is a compound group consisting ofcaprolactone-modified dipentaerythritol hexaacrylate, polyethoxylatedtetramethylol methane tetraacrylate, ethylene oxide-modified bisphenol Adiacrylate, caprolactone-modified hydroxy pivalic acid neopentyl glycoldiacrylate, polypropylene glycol diacrylate[CH₂═CH—CO—(OC₃H₆)n-OCOCH═CH₂ (n≈12)], hydroxyethyl acryl amide,trimethylol propane trimethacrylate, and tricyclodecane dimethanoldimethacrylate, and

the compound group (B) is a compound group consisting of ethyleneoxide-modified phenol acrylate, isostearyl acrylate, ethyleneoxide-modified trimethylol propane trimethacrylate, stearylmethacrylate, and glycerin dimethacrylate.

Advantageous Effects of Invention

The present invention can provide a photopolymerizable inkjet ink, whichhas no problem of skin sensitization, and achieve both low viscosity andimproved curing property.

Further, printed matter produced with the ink of the present inventionhas no problem of skin sensitization even if an uncured monomercomponent is remained and therefore safe, and skin sensitization is notcaused even when the printed matter is touched with hands or fingers.Accordingly, safe printed matter can be provided.

BRIEF. DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram illustrating one example of an ink bag ofthe ink cartridge of the present invention.

FIG. 2 is a schematic diagram illustrating one example of the inkcartridge of the present invention housing an ink bag.

FIG. 3 is a schematic diagram illustrating one example of the inkjetrecording device (printer) of the present invention.

DESCRIPTION OF EMBODIMENTS

(Photopolymerizable Inkjet Ink)

The photopolymerizable inkjet ink (may also referred to merely as “ink”hereinafter) of the present invention contains at leastphotopolymerizable monomers, and may further contain other components,such as a photoradical polymerization initiator, a polymerizationaccelerator, and a colorant, if necessary.

<Photopolymerizable Monomers>

The photopolymerizable monomers contain at least one selected from thefollowing compound group (A), compounds of which are negative for skinsensitization, and at least one selected from the following compoundgroup (B), compounds of which are negative for skin sensitization, andmay further contain at least on selected from the following compoundgroup (C), and other photopolymerizable monomers, if necessary.

Compound group (A): a compound group consisting of caprolactone-modifieddipentaerythritol hexaacrylate, polyethoxylated tetramethylol methanetetraacrylate, ethylene oxide-modified bisphenol A diacrylate,caprolactone-modified hydroxy pivalic acid neopentyl glycol diacrylate,polypropylene glycol diacrylate [CH₂═CH—CO—(OC₃H₆)n-OCOCH═CH₂ (n≈12)],hydroxyethyl acryl amide, trimethylol propane trimethacrylate, andtricyclodecane dimethanol dimethacrylate

Compound group (B): a compound group consisting of ethyleneoxide-modified phenolacrylate, isostearyl acrylate, ethyleneoxide-modified trimethylol propane trimethacrylate, stearylmethacrylate, and glycerin dimethacrylate

Compound group (C): a compound group consisting of triethylene glycoldivinyl ether, hydroxybutyl vinyl ether, ethyl vinyl ether, t-butylmethacrylate, n-pentyl methacrylate, and n-hexyl methacrylate

Note that, “n≈12” in the description of the polypropylene glycoldiacrylate [CH₂═CH—CO—(OC₃H₆)n-OCOCH═CH₂ (n≈12)] means that the averagevalue of “n” is 12 though compounds having different values of “n” arepresent as a mixture in the polypropylene glycol diacrylate. Similarly,the “n≈” described in the descriptions below also means the averagevalue.

The present invention will be explained in details hereinafter.

Conventionally, there has not been a photopolymerizable monomer that canbe used as a material for a photopolymerizable inkjet ink and isnegative for skin sensitization, and that can achieve both sufficientlylow viscosity and sufficient curing property when used alone. Withmonomers that are negative for skin sensitization, studied is a methodfor blending the monomer having excellent curing property but havinghigh viscosity, and the monomer having low viscosity but havinginsufficient curing property with a desirable balance and using themixture.

As a result, the compound group (B) has been found as photopolymerizablemonomers being negative for skin sensitization and having low viscosity.Then, both low viscosity and improved curing property have beensuccessfully achieved by using the compound group (B) in combinationwith the compound group (A), which is previously discovered, andcompounds of which are negative for skin sensitization, and havedesirable curing property but having high viscosity.

An amount of the compound group (A) in the photopolymerizable monomersis not appropriately selected depending on the intended purpose withoutany limitation, but it is preferably 5% by mass to 95% by mass, morepreferably 10% by mass to 50% by mass. An amount of the compound group(B) in the photopolymerizable monomers is not appropriately selecteddepending on the intended purpose without any limitation, but it ispreferably 5% by mass to 95% by mass, more preferably 10% by mass to 85%by mass.

A blending ratio (A)/(B) (mass ratio) of the compound group (A) and thecompound group (B) is not appropriately selected depending on theintended purpose without any limitation, but it is preferably 5/95 to95/5, more preferably 15/85 to 85/15.

Here, the photopolymerizable monomer negative for skin sensitizationrefers to a compound that is evaluated as at least one of the followingskin sensitization evaluations (1) to (3):

-   (1) a compound having a Stimulation Index (SI value) of less than 3,    where the Stimulation Index indicates the extent of sensitization as    measured by a skin sensitization test based on the LLNA (Local Lymph    Node Assay);-   (2) a compound evaluated as “negative for skin sensitization” or “no    skin sensitization” in its MSDS (Material Safety Data Sheet); and-   (3) a compound evaluated as “negative for skin sensitization” or    “without skin sensitization” in literature [e.g., Contact Dermatitis    8 223-235 (1982)].

Regarding the above (1), the compound having a SI value of less than 3is considered negative for skin sensitization as described inliteratures, for example, “Functional Material” (Kino Zairyou) 2005,September, Vol. 25, No. 9, p. 55. The lower SI value means lower skinsensitization. Thus, in the present invention, a monomer or an oligomerhaving lower SI value is preferably used. The SI value of the monomer orthe oligomer used is less than 3, preferably 2 or lower, more preferably1.6 or lower.

<<Compound Group (C)>>

As for the compound group (C), vinyl ethers negative for skinsensitization are used, and examples of the compound group (C) include acompound group consisting of triethylene glycol divinyl ether,hydroxybutyl vinyl ether, ethyl vinyl ether, t-butyl methacrylate,n-pentyl methacrylate, and n-hexyl methacrylate.

The ink of the present invention preferably contains, as aphotopolymerizable monomer, at least one selected from the compoundgroup (C), compounds of which are negative for skin sensitization.

At least one selected from the compound group is not appropriatelyselected depending on the intended purpose without any limitation, butamong the compound group (C), triethylene glycol divinyl ether ispreferable, because it is sufficiently low viscous, has a boiling pointthat is not excessively low, and is easily handled under ambienttemperature and pressure. Moreover, t-butyl methacrylate, n-pentylmethacrylate, and n-hexyl methacrylate are also preferable because theyare negative for skin sensitization and have sufficiently low viscosity.An amount of the compound group (C) in the photopolymerizable monomersis not appropriately selected depending on the intended purpose withoutany limitation, but it is preferably 10% by mass to 90% by mass, morepreferably 40% by mass to 60% by mass.

<<Other Photopolymerizable Monomer>>

Moreover, the following (meth)acrylates, (meth)acryl amides, and vinylethers can be used in combination as other photopolymerizable monomers,even through they have a problem of skin sensitization in some degreesas used alone, or skin sensitization thereof is not confirmed, as longas an ink as a whole does not have a problem.

Examples of other photopolymerizable monomers include ethylene glycoldi(meth)acrylate, hydroxypivalic acid neopentyl glycol di(meth)acrylate,γ-butyrolactone acrylate, isobornyl(meth)acrylate, formulatedtrimethylol propane mono(meth)acrylate, polytetramethylene glycoldi(meth)acrylate, trimethylol propane (meth)acrylic acid benzoate,diethylene glycol diacrylate, triethylene glycol di(meth)acrylate,tetraethylene glycol di(meth)acrylate, polyethylene glycol diacrylates[CH₂═CH—CO—(OC₂H₄)n-OCOCH═CH₂ (n≈4)], [CH₂═CH—CO—(OC₂H₄)n-OCOCH═CH₂(n≈9)], [CH₂═CH—CO—(OC₂H₄)n-OCOCH═CH₂ (n≈14)],[CH₂═CH—CO—(OC₂H₄)n-OCOCH═CH₂ (n≈23)], dipropylene glycoldi(meth)acrylate, tripropylene glycol di(meth)acrylate, polypropyleneglycol dimethacrylate [CH₂═C(CH₃)—CO—(OC₃H₆)n-OCOCH(CH₃)═CH₂ (n≈7)],1,3-butanediol di(meth)acrylate, 1,4-butanediol diacrylate,1,6-hexanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate,neopentyl glycol di(meth)acrylate, tricyclodecane dimethanol diacrylate,propylene oxide-modified bisphenol A di(meth)acrylate, polyethyleneglycol di(meth)acrylate, dipentaerythritol hexa(meth)acrylate,(meth)acryloyl morpholine, 2-hydroxypropyl(meth)acryl amide, propyleneoxide-modified tetramethylol methane tetra(meth)acrylate,dipentaerythritol hydrorxypent-a(meth)acrylate, caprolactone-modifieddipentaerythritol hydroxypenta(meth)acrylate, ditrimethylol propanetetra(meth)acrylate, pentaerythritol tetra(meth)acrylate, trimethylolpropane triacrylate, ethylene oxide-modified trimethylol propanetriacrylate, propylene oxide-modified trimethylol propanetri(meth)acrylate, caprolactone-modified trimethylol propanetri(meth)acrylate, pentaerythritol tri(meth)acrylate,tris(2-hydroxyethyl)isocyanurate tri(meth)acrylate, ethoxylatedneopentyl glycol di(meth)acrylate, propylene oxide-modified neopentylglycol di(meth)acrylate, propylene oxide-modified glyceryltri(meth)acrylate, polyester di(meth)acrylate, polyestertri(meth)acrylate, polyester tetra(meth)acrylate, polyesterpenta(meth)acrylate, polyester poly(meth)acrylate, N-vinyl caprolactam,N-vinyl pyrrolidone, N-vinyl formamide, polyurethane di(meth)acrylate,polyurethane tri(meth)acrylate, polyurethane tetra(meth)acrylate,polyurethane penta(meth)acrylate, polyurethane poly(meth)acrylate,cyclohexane dimethanol divinyl ether, cyclohexane dimethanol monovinylether, hydroxyethyl vinyl ether, diethylene glycol monovinyl ether,diethylene glycol divinyl ether, dicyclopentadiene vinyl ether,tricyclodecane vinyl ether, benzyl vinyl ether, and ethyloxtacene methylvinyl ether.

<Other Components>

<<Photoradical Polymerization Initiator>>

The ink of the present invention preferably contains a photoradicalpolymerization initiator. The photoradical polymerization initiator isnot appropriately selected depending on the intended purpose without anylimitation, but the photoradical polymerization initiator is preferablyselected from those negative for skin sensitization.

The photoradical polymerization initiator negative for skinsensitization is appropriately selected depending on the intendedpurpose without any limitation, provided that it is compounds of any ofthe skin sensitization evaluations (1) to (3), and examples thereofinclude 2-dimethylamino-2-(4-methylbenzyl)-1-(4-morpholin-4-yl-phenyl)butan-1-one, 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one,2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)butanone-1, and2,4-diethyl thioxanthone. These may be used alone or in combination.

The (meth)acrylic acid ester, the (meth)acryl amide, and the vinyl etherare known to have cationic polymerization property as well.Photocationic polymerization initiators are generally expensive andgenerate a trace amount of a strong acid even in the state where theyare not irradiated with light. Thus, it is necessary to take specialcares such as imparting acid resistance to the ink supply channel of aprinter, imposing limitation on the choice of the constituent members ofthe printer. In contrast, the ink of the present invention can containthe photoradical polymerization initiator that is inexpensive andgenerates no strong acid. Thus, it is possible to produce an ink at lowcost, and also it is easy to choice the constituent members of aprinter. Needless to say, when using quite high energy light source suchas electron beams, α rays, β rays, γ rays or X rays, polymerizationreaction proceeds without polymerization initiator. This is aconventionally known matter, and not described in detail in the presentinvention.

The photoradical polymerization initiator includes, for example, aself-cleaving photopolymerization initiator and a hydrogen-abstractingpolymerization initiator.

Examples of the self-cleaving photopolymerization initiator include2,2-dimethoxy-1,2-diphenylethan-1-one, 1-hydroxycyclohexyl phenylketone, 2-hydroxy-2-methyl-1-phenylpropan-1-one,1-[4-(2-hydroxyethoxyl)-phenyl]-2-hydroxy-2-methyl-1-propan-1-one,2-hydroxy-1-{4-[4-(2-hydroxy-2-methylpropionyl)benzyl]phenyl}-2-methyl-1-propan-1-one,phenylglyoxylic acid methyl ester,2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one,2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)butanone-1,2-dimethylamino-2-(4-methylbenzyl)-1-(4-morpholin-4-yl-phenyl)butan-1-one, bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide,bis(2,6-dimethoxybenzoyl)-2,4,4-trimethyl-pentylphosphine oxide,2,4,6-trimethylbenzoylphosphine oxide,1,2-octanedion-[4-(phenylthio)-2-(o-benzoyloxime)],ethanone-1-[9-ethyl-6-(2-methylbenzoyl)-9H-carbazol-3-yl]-1-(O-acetyloxime)and [4-(methylphenylthio)phenyl]phenylmethanone.

Examples of the hydrogen-abstracting polymerization initiator include:benzophenone compounds such as benzophenone, methylbenzophenone,methyl-2-benzoylbenzoate, 4-benzoyl-4′-methyldiphenyl sulfide andphenylbenzophenone; and thioxanthone compounds such as2,4-diethylthioxanthone, 2-chlorothioxanthone, isopropylthioxanthone and1-chloro-4-propylthioxanthone.

<<Polymerization Accelerator>>

Amines may be used as a polymerization accelerator in combination withthe photoradical polymerization initiator.

Examples of the polymerization accelerator includep-dimethylaminobenzoate, 2-ethylhexyl p-dimethylaminobenzoate, methylp-dimethylaminobenzoate, 2-dimethylaminoethyl benzoate and butoxyethylp-dimethylaminobenzoate.

<<Colorant>>

The ink may contain a colorant, as desired. The colorant isappropriately selected from conventional inorganic pigments, organicpigment, and various color pigments (e.g. black pigments, yellowpigments, magenta pigments, cyan pigment, and white pigments) dependingon the intended purpose without any limitation.

As for black pigments, those such as carbon black produced by thefurnace method or the channel method can be used.

As for yellow pigments, for example, the following Pig. Yellow seriespigments can be used: Pig. Yellow 1, Pig. Yellow 2, Pig. Yellow 3, Pig.Yellow 12, Pig. Yellow 13, Pig. Yellow 14, Pig. Yellow 16, Pig. Yellow17, Pig. Yellow 73, Pig. Yellow 74, Pig. Yellow 75, Pig. Yellow 83, Pig.Yellow 93, Pig. Yellow 95, Pig. Yellow 97, Pig. Yellow 98, Pig. Yellow114, Pig. Yellow 120, Pig. Yellow 128, Pig. Yellow 129, Pig. Yellow 138,Pig. Yellow 150, Pig. Yellow 151, Pig. Yellow 154, Pig. Yellow 155, andPig. Yellow 180.

As for magenta pigments, for example, the following Pig. Red seriespigments can be used: Pig. Red 5, Pig. Red 7, Pig. Red 12, Pig. Red 48(Ca), Pig. Red 48 (Mn), Pig. Red 57 (Ca), Pig. Red 57:1, Pig. Red 112,Pig. Red 122, Pig. Red 123, Pig. Red 168, Pig. Red 184, Pig. Red 202,and Pig. Violet 19.

As for cyan pigments, for example, the following Pig. Blue seriespigments can be used: Pig. Blue 1, Pig. Blue 2, Pig. Blue 3, Pig. Blue15, Pig. Blue 15:3, Pig. Blue 15:4, Pig. Blue 16, Pig. Blue 22, Pig.Blue 60, Vat Blue 4, and Vat Blue 60.

As for the white pigment, for example, usable are sulfuric acid salts ofalkaline earth metals such as barium sulfate, carbonic acid salts ofalkaline earth metals such as calcium carbonate, silica such as finesilicic acid powder and synthetic silicic acid salts, calcium silicate,alumina, alumina hydrate, titanium oxide, zinc oxide, talc and clay.

In addition, various inorganic or organic pigments may optionally beused considering, for example, physical properties of the ink.

Furthermore, a polymerization inhibitor, a higher-fatty-acid, siliconeor fluoro surfactant, or a polar group-containing polymeric pigmentdispersing agent may optionally be used. Examples of the polymerizationinhibitor include 4-methoxy-1-naphthol, methylhydroquinone,hydroquinone, t-butylhydroquinone, di-t-butylhydroquinone, methoquinone,2,2′-dihydroxy-3,3′-di(α-methylcyclohexyl)-5,5′-dimethyldiphenylmethane, p-benzoquinone, di-t-butylbutyl diphenylamine,9,10-di-n-butoxyanthracene,4,4′-[1,10-dioxo-1,10-decanediylbis(oxy)]bis[2,2,6,6-tetramethyl]-1-piperidinyloxy.

The physical properties of the ink are appropriately selected dependingon the intended purpose without any limitation, but they are desirablymatched to specification required for an inkjet ejection head as used.Various ejection heads are on the marked from numerous manufacturers,and among them, there are ejection heads having a function of adjustingtemperature over a wide temperature range. Considering such markettrends, the viscosity of the ink at temperature of 25° C. is preferably2 mPa·s to 150 mPa·s. In the case where the ink is ejected at 25° C.,the viscosity of the ink is preferably 5 mPa·s to 18 mPa·s. As mentionedearlier, it is possible to use the temperature adjustment function ofthe ejection head. In the case where the viscosity of the ink is toohigh at 25° C., the viscosity thereof can be reduced by optionallyheating the head. Assuming that the heating condition is 60° C., in theaforementioned case, the viscosity of the ink at 60° C. is preferably 2mPa·s to 20 mPa·s, more preferably 5 mPa·s to 18 mPa·s.

Accordingly, the low viscosity of the ink can be achieved as long as theviscosity of the ink falls into either a range of 5 mPa·s to 18 mPa·s at25° C., or a range of 2 mPa·s to 20 mPa·s at 60° C.

The light dose required for curing is appropriately selected dependingon the intended purpose without any limitation, but the less energy ismore preferable in view of energy saving. When the ink is designed tocure with radiation of very weak light, the ink is reacted with lightleaked from a light source or light from indoor lighting to cure at agas-liquid interface of the ink in an inkjet nozzle of the ejectionhead, which may cause clogging of the nozzle. It is often a case thatthis problem can be avoided by optimizing a design of a printer, but inany case, it is not preferable that the ink has high reactivity forcuring. Accordingly, the light dose required for curing is preferably 5mJ/cm² to 10,000 mJ/cm², more preferably 10 mJ/cm² to 1,000 mJ/cm², andeven more preferably 10 mJ/cm² to 200 mJ/cm². When the light doserequired for curing is within the aforementioned preferable range, itcan be said that the curing property of the ink is improved.

(Ink Cartridge)

The ink cartridge of the present invention contains thephotopolymerizable inkjet ink of the present invention, and a container,and may further contain other members, such as an ink bag, if necessary.

The ink of the present invention is housed in the container, which canbe used as an ink cartridge. With this form, users do not have todirectly touch the ink during works such as exchange of the ink, andthus they are not concerned with staining of their fingers, hands orclothes. In addition, it is possible to prevent interfusion of foreignmatter such as dust into the ink.

The container is not particularly limited, and the shape, structure,size and material thereof may be appropriately selected depending on theintended purpose. For example, the container is preferably selected fromthose having at least an ink bag formed of an aluminum laminate film, ora resin film.

The ink cartridge will be described referring to FIGS. 1 and 2. FIG. 1is a schematic diagram illustrating an example of an ink bag 241 of anink cartridge. FIG. 2 is a schematic diagram illustrating an inkcartridge 200 containing the ink bag 241 illustrated in FIG. 1 and acartridge case 244, which is one example of the container, and housesthe ink bag 241.

As illustrated in FIG. 1, the ink bag 241 is filled with the ink byinjecting the ink from an ink inlet 242. After removal of air presentinside the ink bag 241, the ink inlet 242 is sealed by fusion bonding.At the time of use, a needle attached to the main body of the device isinserted into an ink outlet 243 formed of a rubber member to supply theink to the device therethrough. The ink bag 241 is formed of a wrappingmember such as an air non-permeable aluminum laminate film. Asillustrated in FIG. 2, the ink bag 241 is typically housed in a plasticcartridge case 244, which is then detachably mounted in use to variousinkjet recording devices as the ink cartridge 200.

The ink cartridge of the present invention is preferably detachablymounted to inkjet recording devices. The ink cartridge can simplify therefill and exchange of the ink to improve workability.

(Inkjet Recording Device)

The inkjet recording device of the present invention contains at leastan ink applying unit configured to apply a photopolymerizable inkjet inkon a base material to be printed, and may further contain other unitssuch as an ink curing unit configured to cure the ink on the basematerial to be printed, if necessary.

The photopolymerizable inkjet ink is the photopolymerizable inkjet inkof the present invention. Moreover, the ink applying unit preferablycontain the ink cartridge of the present invention mounted therein.

FIG. 3 is a schematic diagram illustrating one example of the inkjetrecording device (printer) of the present invention.

FIG. 3 illustrates an example that forms a color image in the followingmanner. Specifically, printing units 3 (i.e., printing units 3 a, 3 b, 3c and 3 d for respective colors (e.g., yellow, magenta, cyan, and black)eject color inks (yellow, magenta, cyan and black) on a base material tobe printed 2 (which is conveyed from left to right in FIG. 3, and may bereferred to as “base” hereinafter) fed from a base material feed roller1, and light (UV rays) is applied from UV light sources (curing lightsources) 4 a, 4 b, 4 c and 4 d to the corresponding color inks forcuring. Each of the printing units 3 a, 3 b, 3 c and 3 d has a heatingmechanism at an ink ejecting portion thereof, and a cooling mechanism ata base holding portion thereof (i.e., a portion above or under the basein FIG. 3). The heating mechanism serves to heat an ink with a highviscosity so as to decrease its viscosity. The cooling mechanism servesto cool the base to about room temperature in a contact or non-contactmanner, if necessary. In the case where the ink is heated for ejection,when the printing area of the previously printed color is small and theconveyance speed of the base is low, the base material is naturallycooled and kept at about room temperature in the subsequent printing.However, when the printing area of the previously printed color is largeand the conveyance speed of the base is high, the base increases intemperature to potentially cause variation between the respective colorinks in behaviors such as wetting and spreading of the ink droplets thathave been jetted onto the base or the previously jetted ink, to therebyadversely affect image formation. Thus, if necessary, the coolingmechanism may be provided for keeping a base at about room temperature.

The base material 2 used is, for example, paper, a film, a metal or acomposite material thereof. The base material 2 illustrated in FIG. 3 isa roll but may be a sheet. In addition, the base material may besubjected to double-side printing as well as single-side printing.

When UV rays are applied to each of the color inks for every printingprocess, the color inks are satisfactorily cured. In order to achievehigh-speed printing, the UV light sources 4 a, 4 b and 4 c may belowered in output power or may be omitted, so that the UV light source 4d is made to apply a sufficient dose of UV rays to a composite printedimage formed of a plurality of colors. In addition, for realizing energysaving and cost reduction, LED light sources, which have recently beenused practically for printing of photopolymerizable inks, may be usedinstead of conventionally used light sources such as high-pressuremercury lamps and metal halide lamps. In FIG. 3, reference numeral 5denotes a processing unit and reference numeral 6 denotes a wind-up rollfor printed products.

EXAMPLES

The present invention will next be described by way of Examples, whichshould not be construed as limiting the present invention thereto.

Examples 1 to 19

The materials of the following compound groups (A) to (C) were mixedtogether at the blending ratio (unit for the numeric value was parts bymass) of the corresponding columns of Examples and Comparative Examplesshown in Table 3, to thereby obtain inks.

-   Compound group (A): (meth)acrylic acid ester and/or (meth)acryl    amide, which is negative for skin sensitization (of high viscosity,    but excellent curing property)-   Compound group (B): (meth)acrylic acid ester and/or (meth)acryl    amide, which is negative for skin sensitization (of low viscosity)-   Compound group (C): triethylene glycol divinyl ether, t-butyl    methacrylate, n-pentyl methacrylate, and n-hexyl methacrylate, each    of which are negative for skin sensitization (of sufficiently low    viscosity)-   Compound group (D): photoradical polymerization initiator negative    for skin sensitization

The details of A1 to A8, B1 to B5, C1 to C4, and D1 to D4 in Table 3 areas follows. The value in parentheses after each product name is “SIvalue” as measured by the LLNA test described in the above skinsensitization evaluation (1). The description “negative for skinsensitization” or “no skin sensitization” after each product name meansthat the product is evaluated as “negative for skin sensitization” or“no skin sensitization” in the MSDS (Material Safety Data Sheet)described in the above skin sensitization evaluation (2) or theliterature described in the above skin sensitization evaluation (3), andMSDS or literature used for the evaluation standard, and the test methodused are also depicted.

The evaluation method of the SI value will be described below in detail.

-   A1: Caprolactone-modified dipentaerythritol hexaacrylate, DPCA-60,    manufactured by NIPPON KAYAKU Co. Ltd. (negative for skin    sensitization, evaluated in MSDS, test method: OECD test guideline    406)-   A2: Polyethoxylated tetramethylol methane tetraacrylate, ATM-35E    (1.7), manufactured by Shin-Nakamura Chemical Co., Ltd.-   A3: Ethylene oxide-modified bisphenol A diacrylate, BPE-10 (1.2),    manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.-   A4: Caprolactone-modified neopentylglycol hydroxypivalate    diacrylate, HX-620 (0.9), manufactured by NIPPON KAYAKU Co. Ltd.-   A5: Polypropylene glycol diacrylate [CH₂═CH—CO—(OC₃H₆)n-OCOCH═CH₂    (n≈12)], M-270 (1.5), manufactured by Toagosei Chemical CO., LTD.-   A6: Hydroxyethyl acryl amide, HEAA manufactured by KOHJIN Co., Ltd.    (no skin sensitization, evaluated in MSDS, test method: OECD test    guideline 429)-   A7: Trimethylol propane trimethacrylate, SR350 (1.9), manufactured    by Sartomer Co.-   A8: Tricyclodecane dimethanol dimethacrylate, DCP (1.3),    manufactured by Shin-Nakamura Chemical Co., Ltd.-   B1: Ethylene oxide-modified phenol acrylate, M-102 (0.7),    manufactured by Toagosei Chemical CO., LTD.-   B2: Isostearyl acrylate, S-1800A (1.4), manufactured by    Shin-Nakamura Chemical Co., Ltd.-   B3: Ethylene oxide-modified trimethylol propane trimethacrylate,    TMPT-3EO (1.0), manufactured by Shin-Nakamura Chemical Co., Ltd.-   B4: Stearyl methacrylate, S (1.2), manufactured by Shin-Nakamura    Chemical Co., Ltd.-   B5: Glycerin dimethacrylate, 701 (1.2), manufactured by    Shin-Nakamura Chemical Co., Ltd.-   C1: Triethylene glycol divinyl ether, manufactured by BASF (negative    for skin sensitization, evaluated in MSDS, test method: OECD test    guideline 406)-   C2: t-Butyl methacrylate, Light Ester TB, manufactured by KYOEISHA    CHEMICAL CO., LTD. (negative for skin sensitization, evaluated in    the literature: Contact Dermtitis 8 223-235 (1982), test method:    maximization)-   C3: n-Pentyl methacrylate, manufactured by Tokyo Science Corp.    (negative for skin sensitization, evaluated in the literature:    Contact Dermtitis 8 223-235 (1982), test method: maximization)-   C4: n-Hexyl methacrylate, TOKYO CHEMICAL INDUSTRY CO., LTD.    (negative for skin sensitization, evaluated in the literature:    Contact Dermtitis 8 223-235 (1982), test method: maximization)-   D1:    2-Dimethylamino-2-(4-methylbenzyl)-1-(4-morpholin-4-yl-phenyl)butan-1-one    (no skin sensitization, evaluated in MSDS, test method: OECD test    guideline 406)-   D2: 2-Methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one (no    skin sensitization, evaluated in MSDS, test method: OECD test    guideline 406)-   D3: 2-Benzyl-2-dimethylamino-1-(4-morpholinophenyl) butanone-1 (no    skin sensitization, evaluated in MSDS, test method: OECD test    guideline 406)-   D4: Equimolar mixture of 2,4-diethyl thioxanthone (1.4) and    p-dimethylaminobenzoic acid-2-ethylhexyl (no skin sensitization,    evaluated in MSDS, test method: OECD test guideline 406)    <Measuring Method of SI Value>

According to the skin sensitization test based on the LLNA (Local LymphNode Assay), the SI value was measured in the below described manner.

[Test Material]

<<Positive Control>>

α-Hexylcinnamaldehyde (HCA; product of Wako Pure Chemical Industries,Ltd.) was used as the positive control.

<<Vehicle>>

The vehicle used was a mixture containing the below-listed acetone andolive oil in a ratio by volume of 4/1.

Acetone (product of Wako Pure Chemical Industries, Ltd.)

Olive oil (product of Fudimi Pharmaceutical Co., Ltd.)

<<Animals Used>>

Before treated with the test substances, the positive control or thevehicle control, female mice were acclimated for 8 days including 6-dayquarantine. No abnormalities were found in all the animals during thequarantine/acclimation period. Based on the body weights measured 2 daysbefore the initiation of sensitization, they were categorized into 2groups (4 mice/group) by the body weight stratified random samplingmethod so that the body weight of each individual was within ±20% of theaverage body weight of all the individuals. Each animal was 8 weeks oldto 9 weeks old at the time of the initiation of sensitization. Theanimals remaining after the categorization were excluded from the test.

The animals were individually identified by application of oil ink totheir tale throughout the test period, and also their cages were labeledfor identification.

<<Housing Environment>>

Throughout the housing period including the quarantine/acclimationperiod, the animals were housed in an animal room with barrier system,which was set as follows: 21° C. to 25° C. in temperature, 40% to 70% inrelative humidity, 10 times/hour to 15 times/hour in frequency of aircirculation, and 12 hours in lighting cycle (lighting from 7:00 to19:00).

The housing cages used were those made of polycarbonate, and fouranimals were housed in each cage.

The animals were given ad libitum solid diet for laboratory animals MF(product of Oriental Yeast Co., Ltd.). Also, using a water-supplybottle, they were given ad libitum tap water in which sodiumhypochlorite (PURELOX, product of OYALOX Co., Ltd.) had been added sothat the chlorine concentration was about 5 ppm. Bedding used wasSUNFLAKE (fir tree, shavings obtained with a power planer) (product ofCharles River Inc.). The diet and feeding equipment were sterilized withan autoclave (121° C., 30 min) before use.

The cage and bedding were replaced with new ones at the times of thecategorization and the removal of the auricular lymph node (i.e., thetime when the animals were transferred from the animal room), and thewater-supply bottle and rack were replaced with new ones at the time ofthe categorization.

[Test Method]

<<Group Composition>>

The group composition used for the measurement of the Si value is shownin Table 1.

TABLE 1 Sensitization Number of Sensitization dose Times of animals Testgroup substance (μL/auricle) sensitization (animal No.) Vehicle Vehicleonly 25 Once/day × 3 4 (1-4) control days group Positive 25.0% HCA 25Once/day × 3 4 (5-8) control days group[Preparation]<<Test Substance>>

Table 2 shows the amount of the test substance. The test substance wasweighed in a measuring flask, and the volume of the test substance wasadjusted to 1 mL with a vehicle. The thus-prepared solution was placedin a light-shielded airtight container (made of glass).

TABLE 2 Concentration after adjustment Mass of test (w/v %) substance(g) Test 50.0 0.5 substance<<Positive Control Substance>>

About 0.25 g of HCA was accurately weighed, and a vehicle was added tothe HCA to have the volume of 1 mL, to thereby prepare a 25.0 w/v %solution. The thus-prepared solution was placed in a light-shieldedairtight container (made of glass).

<<BrdU>>

In a measuring flask, 200 mg of 5-bromo-2′-deoxyuridine (BrdU, productof NACALAI TESQUE, INC.) was accurately weighed. Then, physiologicalsaline (product of OTSUKA PHARMACEUTICAL CO., LTD.) was added to themeasuring flask, and dissolved through application of ultrasonic waves.The volume of the resultant solution was adjusted to 20 mL to prepare a10 mg/mL solution (BrdU preparation). The thus-prepared solution wassterilized through filtration with a sterilized filtration filter andplaced in a sterilized container.

<<Preparation Day and Storage Period>>

The positive control preparation was prepared on the day before theinitiation of sensitization, and stored in a cold place except in use.The vehicle and the test substance preparations were prepared on the dayof sensitization. The BrdU solution was prepared 2 days beforeadministration and stored in a cold place until the day ofadministration.

[Sensitization and Administration of BrdU]

<<Sensitization>>

Each (25 μL) of the test substance preparations, the positive controlpreparation or the vehicle was applied to both the auricles of eachanimal using a micropipettor. This treatment was performed once a dayfor three consecutive days.

<<Administration of BrdU>>

About 48 hours after the final sensitization, the BrdU preparation (0.5mL) was intraperitoneally administered once to each animal.

[Observation and Examination]

<<General Conditions>>

All the animals used for the test were observed once or more times a dayfrom the day of the initiation of sensitization to the day of theremoval of the auricular lymph node (i.e., the day when the animals weretransferred from the animal room). Notably, the observation day wascounted from the day of the initiation of sensitization being regardedas Day 1.

<<Measurement of Body Weights>>

The body weight of each animal was measured on the day of the initiationof sensitization and on the day of the removal of the auricular lymphnode (i.e., the day when the animals were transferred from the animalroom). Also, the average of the body weights and the standard errorthereof were calculated for each group.

<<Removal of Auricular Lymph Node and Measurement of Mass Thereof>>

About 24 hours after the administration of BrdU, the animals wereallowed to undergo euthanasia, and their auricular lymph nodes weresampled. The surrounding tissue of each auricular lymph node wasremoved, and the auricular lymph nodes from both the auricles werecollectively weighed. Also, the average of the weights of the auricularlymph nodes and the standard error thereof were calculated for eachgroup. After the measurement of the weights, the auricular lymph nodesof each individual were stored in a frozen state using a BIO MEDICALFREEZER set to −20° C.

<<Measurement of BrdU Intake>>

After returned to room temperature, the auricular lymph nodes weremashed with the gradual addition of physiological saline, and suspendedtherein. The thus-obtained suspension was filtrated and then dispensedinto the wells of a 96-well microplate, with 3 wells being used perindividual. The thus-dispensed suspensions were measured for intake ofBrdU by the ELISA method. The reagents used were those of a commerciallyavailable kit (Cell Proliferation ELISA, BrdU colorimetric, Cat. No.1647229, product of Roche Diagnostics Inc.). A multiplate reader(FLUOSTAR OPTIMA, product of BMG LABTECH Inc.) was used to measure theabsorbance of each well (OD: 370 nm to 492 nm, the intake of BrdU), andthe average of the absorbance of the 3 wells for each individual wasused as the measurement of BrdU for the individual.

[Evaluation of Results]

<<Calculation of Stimulation Index (SI)>>

As shown in the following formula, the measurement of BrdU intake foreach individual was divided by the average of the measurements of BrdUintake in the vehicle control group to calculate the SI value for theindividual. The SI value of each test group was the average of the SIvalues of the individuals. Also, the standard error of the SI values wascalculated for each test group. Notably, the SI value was rounded at thesecond decimal place and shown to the first decimal place.

${SI} = \frac{\begin{matrix}{{Average}\mspace{14mu}{of}\mspace{14mu}{measurements}\mspace{14mu}{of}\mspace{14mu}{BrdU}} \\{{intake}\mspace{14mu}{for}\mspace{14mu}{each}\mspace{14mu}{individual}\mspace{14mu}\left( {{average}\mspace{14mu}{of}\mspace{14mu} 3\mspace{14mu}{wells}} \right)}\end{matrix}}{\begin{matrix}{{Average}\mspace{14mu}{of}\mspace{14mu}{measurements}\mspace{14mu}{of}\mspace{14mu}{BrdU}\mspace{14mu}{intake}\mspace{14mu}{in}} \\{{the}\mspace{14mu}{vehicle}\mspace{14mu}{control}\mspace{14mu}{group}\mspace{14mu}\left( {{average}\mspace{14mu}{of}\mspace{14mu} 4\mspace{14mu}{animals}} \right)}\end{matrix}}$

Each of the above-prepared inks was measured for viscosities (mPa·s) at25° C. and 60° C., and light dose required for curing (mJ/cm²). Theresults are shown in Table 3.

The viscosities at 25° C. and 60° C. were measured with acone-plate-type rotary viscometer (product of TOKI SANGYO CO., LTD.)with the temperature of circulating water being constantly set to 25° C.and 60° C. The temperature of 25° C. is a temperature generallyconsidered room temperature. The temperature of 60° C. is a temperatureset considering the specification of a commercially available inkjetejection head, such as GEN4 (product of Ricoh Printing Systems, Ltd.),that can be heated.

The curing property of the inks was evaluated as follows. Specifically,each ink was jetted on a commercially available polyethyleneterephthalate (PET) film and irradiated with light using a UVirradiating device LH6 (product of Fusion Systems Japan Co., Ltd.).

An aluminum pouch bag having a shape illustrated in FIG. 1 was chargedwith the ink, and hermetically sealed so as to avoid inclusion of airbubbles. The hermetically sealed pouch bag containing the ink was housedin a plastic cartridge as illustrated in FIG. 2. This cartridge wasmounted to a casing adapted for housing it. In the casing, an ink flowchannel was provided from the cartridge to a GEN4 head (product of RicohPrinting Systems, Ltd.). The ink was jetted through the ink flow channelto form, on the film, a solid coated film.

The thus-formed solid coated film was irradiated with light of thewavelength region corresponding to the UVA region, with the light dosebeing changed stepwise to 1,000, 500, 200, 100, 50, 20 and 10 (mJ/cm²).Whether the solid coated film turned into the non-sticky state wasjudged by touching it with a finger, and the solid coated film wasjudged as being cured when it turned into the non-sticky state. Theminimum integrated light dose required for curing the solid coated filmis shown as the light dose required for curing. The inks that requireless integrated light dose have better curing property.

TABLE 3 Comp. Ex. Example Material 1 1 2 3 4 5 6 7 8 9 A A1 15 15 10 1010 5 A2 10 A3 5 5 5 A4 5 A5 85 5 5 A6 5 5 A7 50 40 40 A8 5 5 B B1 85 8580 80 85 85 B2 5 B3 45 50 45 B4 5 B5 5 5 C C1 C2 C3 C4 D D1 10 10 10 1010 10 10 20 20 20 D2 D3 D4 Carbon black*² Viscosity (25° C.) 120 67 6159 61 56 60 130 133 132 Viscosity (60° C.) 30 14 12 12 12 11 13 15 15 15Ejection tem. 60 60 60 60 60 60 60 60 60 60 from head (° C.) Light dosefor *1 50 50 50 50 100 100 1,000 1,000 1,000 curing Example Material 1011 12 13 14 15 16 17 18 19 A A1 15 15 15 40 40 40 40 40 15 40 A2 A3 A4A5 A6 A7 A8 B B1 85 85 85 10 10 10 10 10 85 10 B2 B3 B4 B5 C C1 50 10 C250 40 50 C3 50 C4 50 D D1 10 5 5 5 5 10 5 D2 10 D3 10 D4 10 Carbonblack*² 4 4 Viscosity (25° C.) 64 69 62 40 12 13 15 14 78 14 Viscosity(60° C.) 13 15 12 11 3 4 5 4 16 4 Ejection tem. 60 60 60 60 25 25 25 2560 25 from head (° C.) Light dose for 100 50 200 100 20 50 100 50 50 20curing *1: incapable of evaluating as ejection could not be carried out*²Carbon black #10, manufactured by Mitsubishi Chemical Corporation,which is in the form of a mixture with a polymer dispersing agent S32000manufactured by Lubrizol Japan Co., with the mass ratio of 3/1 (Carbonblack #10/S32000). The amount of the carbon black above is a blendingamount of Carbon black #10 in the aforementioned mixture.

It was confirmed from the comparison between Comparative Example 1 andExample 1 that the ink could not be ejected due to its high viscositywhen the ink was composed of only the compounds of the compound group(A), but in the case where the ink contained the relatively low viscouscompounds of the compound group (B), the ink was ejected without aproblem by setting the head to the appropriate temperature, and theobtained solid image could be cured by light irradiation.

It was conformed from the comparison between Examples 1 to 6 that theviscosity and curing property could be controlled by appropriatelyadjusting the blending formulation, even in the case where differentacrylates or acryl amides were included in the compound group (A), or inthe case where different acrylates or methacrylates were included in thecompound group (B). Since properties required for an ink are not limitedto viscosity and curing property, and are diverse, such as imagequality, various properties of image coated films, cost, andadaptability to a print process of an inkjet recording device, compoundscan be appropriately selected to satisfy various requirements dependingon the situation.

It was also confirmed that, in the case the compound group (A) and thecompound group (B) in the ink were mainly composed of methacrylates,such as Examples 7 to 9, or in the case where acryl amide or acrylatewas further contained in combination, curing property of such ink wasless desirable compared to those of Examples 1 to 6, but the ink couldbe ejected as ink jets without a problem by setting the head to theappropriate temperature, and the obtained solid image could be cured bylight irradiation.

It was confirmed that viscosity and curing property of the ink could becontrolled when different types of the polymerization initiator wasused, such as in Examples 1, 10 to 12. Similar to the above, compoundscan be appropriately selected to satisfy various requirements dependingon the situation.

It was confirmed that, even in the case where one compound or acombination of compounds of the compound group (C) was used, such as inExamples 13 to 17, the ink could be ejected as inkjets without a problemby setting the heat to the appropriate temperature, and the obtainedsolid image could be cured by light irradiation. Especially in the casewhere t-butyl methacrylate, n-pentyl methacrylate, or n-hexylmethacrylate is used rather than vinyl ether, both low viscosity andhigh curing property of the ink could be achieved better, butmethacrylate also has unique odor. Taking this matter intoconsideration, as mentioned earlier, compounds can be appropriatelyselected to satisfy various requirements depending on the situation.

It was confirmed that, even in the case where the ink contained acolorant, such as in Examples 18 and 19, as long as the ink containedthe relatively low viscous compound of the compound group (B), orfurther contained the compound of the compound group (C), the ink couldbe ejected by setting the heat to the appropriate temperature, and theobtained solid image could be cured by light irradiation.

Embodiments of the present invention are, for example, as follows:

-   <1> A photopolymerizable inkjet ink, containing:

photopolymerizable monomers containing at least one selected from thefollowing compound group (A) compounds of which are negative for skinsensitization, and at least one selected from the following compoundgroup (B) compounds of which are negative for skin sensitization,

wherein the compound group (A) is a compound group consisting ofcaprolactone-modified dipentaerythritol hexaacrylate, polyethoxylatedtetramethylol methane tetraacrylate, ethylene oxide-modified bisphenol Adiacrylate, caprolactone-modified hydroxy pivalic acid neopentyl glycoldiacrylate, polypropylene glycol diacrylate[CH₂═CH—CO—(OC₃H₆)n-OCOCH═CH₂ (n≈12)], hydroxyethyl acryl amide,trimethylol propane trimethacrylate, and tricyclodecane dimethanoldimethacrylate, and

the compound group (B) is a compound group consisting of ethyleneoxide-modified phenolacrylate, isostearyl acrylate, ethyleneoxide-modified trimethylol propane trimethacrylate, stearylmethacrylate, and glycerin dimethacrylate.

-   <2> The photopolymerizable inkjet ink according to <1>, wherein an    amount of the compound group (A) in the photopolymerizable monomers    is 10% by mass to 50% by mass.-   <3> The photopolymerizable inkjet ink according to any of <1> or    <2>, wherein an amount of the compound group (B) in the    photopolymerizable monomers is 10% by mass to 85% by mass.-   <4> The photopolymerizable inkjet ink according to any one of <1> to    <3>, wherein a blending ratio of the compound group (A) and the    compound group (B), which is expressed by a mass ratio of (A)/(B),    is 15/85 to 85/15.-   <5> The photopolymerizable inkjet ink according to any one of <1> to    <4>, wherein the photopolymerizable monomers further contain at    least one selected from the following compound group (C) compounds    of which are negative for skin sensitization,

where the compound group (C) is a compound group consisting oftriethylene glycol divinyl ether, hydroxybutyl vinyl ether, ethyl vinylether, t-butyl methacrylate, n-pentyl methacrylate, and n-hexylmethacrylate.

-   <6> The photopolymerizable inkjet ink according to any one of <1> to    <5>, further comprising a photoradical polymerization initiator.-   <7> The photopolymerizable inkjet ink according to <6>,-   wherein the photoradical polymerization initiator is at least one    selected from the group consisting of    2-dimethylamino-2-(4-methylbenzyl)-1-(4-morpholin-4-yl-phenyl)    butan-1-one,    2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one, and    2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)butanone-1,2,4-diethyl    thioxanthone.-   <8> An ink cartridge, containing:

the photopolymerizable inkjet ink as defined in any one of <1> to <7>;and

a container housing the photopolymerizable inkjet ink.

-   <9> An inkjet recording device, comprising:

the photopolymerizable inkjet ink as defined in any one of <1> to <7>;and

an ink applying unit configured to apply the photopolymerizable inkjetink on a base material to be printed.

REFERENCE SIGNS LIST

-   1: base material feed roller-   2: base material to be printed-   3: printing unit-   3 a: printing unit for a color ink-   3 b: printing unit for a color ink-   3 c: printing unit for a color ink-   3 d: printing unit for a color ink-   4 a: UV light source-   4 b: UV light source-   4 c: UV light source-   4 d: UV light source-   5: processing unit-   6: wind-up roll for printed products-   200: ink cartridge-   241: ink bag-   242: ink inlet-   243: ink outlet-   244: cartridge case

The invention claimed is:
 1. A polymerizable inkjet ink, comprising:photopoymerizable monomers comprising a compound (A) that is negativefor skin sensitization, a compound (B) that is negative for skinsensitization, and a photoradical polymerization initiator wherein thecompound (A) is at least one compound selected from the group consistingof a caprolactone-modified dipentaerythritol hexaacrylate, apolyethoxylated tetramethylol methane tetraacrylate, an ethyleneoxide-modified bisphenol A diacrylate, a caprolactone-modified hydroxypivalic acid neopentyl glycol diacrylate, a polypropylene glycoldiacrylate [CH₂═CH—CO—(OC₃H₆)n-OCOCH═CH₂ (n≈12)], a hydroxyethyl acrylamide, a trimethylol propane trimethacrylate, and a tricyclodecanedimethanol dimethacrylate, the compound (B) is at least one compoundselected from the group consisting of an ethylene oxide-modifiedphenolacrylate, an isostearyl acrylate, and a glycerin dimethacrylate,the photoradical polymerization initiator is 2,4-diethyl thioxanthone,and the ink has a viscosity of from 2 to 150 mPa·s at a temperature of25° C. and a viscosity of from 2 to 20 mPa·s at 60° C.
 2. Thepolymerizable inkjet ink according to claim 1, wherein an amount of thecompound (A) in the photopolymerizable monomers is 10% by mass to 50% bymass.
 3. The polymerizable inkjet ink according to claim 2, wherein anamount of the compound (B) in the photopolymerizable monomers is 10% bymass to 85% by mass.
 4. The polymerizable inkjet ink according to claim3, wherein a blending ratio of the compound (A) and the compound (B),which is expressed by a mass ratio of (A)/(B), is in a range of 15/85 to85/15.
 5. The polymerizable inkjet ink according to claim 2, wherein ablending ratio of the compound (A) and the compound (B), which isexpressed by a mass ratio of (A)/(B), is in a range of 15/85 to 85/15.6. The polymerizable inkjet ink according to claim 2, wherein thephotopolymerizable monomers further comprise a compound (C) that isnegative for skin sensitization, where the compound (C) is at least onecompound selected from the group consisting of triethylene glycoldivinyl ether, hydroxybutyl vinyl ether, ethyl vinyl ether, t-butylmethacrylate, n-pentyl methacrylate, and n-hexyl methacrylate.
 7. Thepolymerizable inkjet ink according to claim 1, wherein an amount of thecompound (B) in the photopolymerizable monomers is 10% by mass to 85% bymass.
 8. The polymerizable inkjet ink according to claim 7, wherein ablending ratio of the compound (A) and the compound (B), which isexpressed by a mass ratio of (A)/(B), is in a range of 15/85 to 85/15.9. The polymerizable inkjet ink according to claim 7, wherein thephotopolymerizable monomers further comprise a compound (C) that isnegative for skin sensitization, where the compound (C) is at least onecompound selected from the group consisting of triethylene glycoldivinyl ether, hydroxybutyl vinyl ether, ethyl vinyl ether, t-butylmethacrylate, n-pentyl methacrylate, and n-hexyl methacrylate.
 10. Thepolymerizable inkjet ink according to claim 1, wherein a blending ratioof the compound (A) and the compound (B), which is expressed by a massratio of (A)/(B), is in a range of 15/85 to 85/15.
 11. The polymerizableinkjet ink according to claim 10, wherein the photopolymerizablemonomers further comprise a compound (C) that is negative for skinsensitization, where the compound (C) is at least one compound selectedfrom the group consisting of triethylene glycol divinyl ether,hydroxybutyl vinyl ether, ethyl vinyl ether, t-butyl methacrylate,n-pentyl methacrylate, and n-hexyl methacrylate.
 12. The polymerizableinkjet ink according to claim 1, wherein the photopolymerizable monomersfurther comprise a compound (C) that is negative for skin sensitization,where the compound (C) is at least one compound selected from the groupconsisting of triethylene glycol divinyl ether, hydroxybutyl vinylether, ethyl vinyl ether, t-butyl methacrylate, n-pentyl methacrylate,and n-hexyl methacrylate.
 13. The polymerizable inkjet ink according toclaim 1, wherein the compound (A) is at least one compound selected fromthe group consisting of a caprolactone-modified hydroxy pivalic acidneopentyl glycol diacrylate, a polypropylene glycol diacrylate[CH₂═CH—CO-(OC₃H₆)n-OCOCH═CH₂ (n≈12)], and a hydroxyethyl acryl amide.14. The polymerizable inkjet ink according to claim 1, wherein ablending ratio of the compound (A) and the compound (B), which isexpressed by a mass ratio of (A)/(B), is 15/85.
 15. The polymerizableinkjet ink according to claim 1, wherein the polymerizable inkjet inkconsists of materials that are negative for skin sensitization.
 16. Anink cartridge, comprising: a polymerizable inkjet ink; and a containerhousing the polymerizable inkjet ink, wherein the polymerizable inkjetink comprises photopolymerizable monomers comprising a compound (A) thatis negative for skin sensitization, a compound (B) that is negative forskin sensitization, and a photoradical polymerization initiator, whereinthe compound (A) is at least one compound selected from the groupconsisting of a caprolactone-modified dipentaerythritol hexaacrylate, apolyethoxylated tetramethylol methane tetraacrylate, an ethyleneoxide-modified bisphenol A diacrylate, a caprolactone-modified hydroxypivalic acid neopentyl glycol diacrylate, a polypropylene glycoldiacrylate [CH₂═CH—CO—(OC₃H₆)n-OCOCH═CH₂ (n≈12)], a hydroxyethyl acrylamide, a trimethylol propane trimethacrylate, and a tricyclodecanedimethanol dimethacrylate, the compound (B) is at least one compoundselected from the group consisting of an ethylene oxide-modifiedphenolacrylate, an isostearyl acrylate, and a glycerin dimethacrylate,the photoradical polymerization initiator is 2,4-diethyl thioxanthone,and the ink has a viscosity of from 2 to 150 mPa·s at a temperature of25° C. and a viscosity of from 2 to 20 mPa·s at 60° C.
 17. An inkjetrecording device, comprising: a polymerizable inkjet ink; and an inkapplying unit configured to apply the polymerizable inkjet ink on a basematerial to be printed, wherein the polymerizable inkjet ink comprisesphotopolymerizable monomers comprising a compound (A) that is negativefor skin sensitization, a compound (B) that is negative for skinsensitization, and a photoradical polymerization initiator, wherein thecompound (A) is at least one compound selected from the group consistingof a caprolactone-modified dipentaerythritol hexaacrylate, apolyethoxylated tetramethylol methane tetraacrylate, an ethyleneoxide-modified bisphenol A diacrylate, a caprolactone-modified hydroxypivalic acid neopentyl glycol diacrylate, a polypropylene glycoldiacrylate [CH₂═CH—CO—(OC₃H₆)n-OCOCH═CH₂ (n≈12)], a hydroxyethyl acrylamide, a trimethylol propane trimethacrylate, and a tricyclodecanedimethanol dimethacrylate, the compound (B) is at least one compoundselected from the group consisting of an ethylene oxide-modifiedphenolacrylate, an isostearyl acrylate, and a glycerin dimethacrylate,the photoradical polymerization initiator is 2,4-diethyl thioxanthone,and the ink has a viscosity of from 2 to 150 mPa·s at a temperature of25° C. and a viscosity of from 2 to 20 mPa·s at 60° C.